Blood pressure monitoring apparatus is well known. It includes a catheter inserted into a patient's blood vessel, a tube connecting the catheter to a transducer, a supply of saline solution connected through the transducer to the catheter and a flush valve connected in the line to the catheter. The system through the catheter is filled with the saline solution, the saline solution forming a static column between the patient's blood vessel and the transducer whereby variations in blood pressure are communicated to the transducer so that the patient's blood pressure is monitored in real time. The flush valve has a capillary through which the saline solution flows, very slowly, to the patient. The slow dripping of the saline solution prevents any clotting of blood in the catheter which might introduce an error into the monitoring of the blood pressure. The flush valve contains a bypass by which a rapid flow of saline solution can be introduced into the system as needed.
It has been conventional to provide a site for withdrawing a blood sample. A stopcock is placed in series between the catheter and the transducer. The stopcock has a port that is normally closed by a solid plug (dead ender), the port being covered by a dust cover. The procedure for drawing a blood sample through the free port on the stopcock has required the following major steps: The stopcock is shifted to block flow of saline solution from the supply and open ports between the catheter and the plugged port. The dust cover is removed and the dead ender plug is moved and carefully set aside to avoid contamination. A syringe is inserted in the opening created by the removal of the dead ender and about 2 cc mixture of blood and saline is withdrawn to remove the saline from the catheter and tube leading to the stopcock so that only blood is present at the free port of the stopcock. A heparinized syringe is inserted into the free stopcock port to withdraw about 1 cc of blood. The stopcock is shifted to open the free port to the saline supply and block the port to the catheter. The free port is flushed, using the flush valve, with saline and the dead ender is replaced. The stopcock is then shifted again to block the free port and connect the catheter to the saline supply. The flush valve then flushes the blood out of the tube and catheter, whereupon the system between the catheter and transducer is filled and ready for resumption of normal monitoring operation.
The foregoing procedure has obvious disadvantages. A number of manipulative steps are required to obtain the blood sample. A number of chances for contamination of the patient's blood are presented in the opening of the port to bring the blood to the stopcock for sampling. Blood usually drips from the sampling port. The exposure of attending people to the patient's blood is a matter of considerable concern because of the possibility of spreading AIDS, hepatitis and the like.